Dual TDMR Head Radial Positioning for HDD Spiral Servo Writing
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Solution Overview
Problem
The spiral-based self-servo writing process in hard disk drives (HDDs) faces challenges with the precision and reliability of writing servo spirals, leading to issues like close spiral spacing and loss of synchronization, which can result in rework or scrapping of HDDs due to velocity variation and overlapping spirals during in-drive spiral writing.
Innovation Solution
The implementation of a system using a magnetic head with first and second read sensors to determine the absolute radial position based on the time interval between detecting a servo spiral, utilizing a lookup table to correlate this interval with pre-computed radial positions, allowing for accurate positioning and synchronization during the spiral-based self-servo writing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If in-drive spiral writing methods are used to write coarse servo spirals, then manufacturing cost and time are reduced, but velocity variation causes spiral spacing differences and potential overlapping
Solution Approach 1:
The patent employs feedback control during the spiral writing process by continuously monitoring the position of previously written spirals and adjusting the actuator velocity in real-time. The servo system reads the written spirals, determines their actual positions, and uses this information to correct velocity variations in subsequent writing operations, ensuring uniform spiral spacing despite initial velocity fluctuations
Solution Approach 2:
The patent performs preliminary positioning by first writing coarse spirals to establish a reference framework, then uses these coarse spirals as a basis for writing finer spirals with more precise spacing. This staged approach allows the system to establish a rough pattern first and then refine it, reducing the impact of velocity variations on final precision
2Productivity
If in-drive spiral writing is used to reduce setup time, then productivity increases, but spiral overlapping and synchronization loss occur
Solution Approach 1:
The system continuously monitors spiral positions during writing and provides feedback to the control system. When a spiral is detected at an unexpected position or when overlapping is anticipated, the feedback mechanism triggers corrective velocity adjustments to prevent synchronization loss and ensure reliable spiral writing
Solution Approach 2:
The patent implements protective measures by maintaining a safety margin between spirals and implementing velocity reduction protocols when approaching critical spacing zones. This cushioning approach prevents overlapping even when velocity variations occur, ensuring that the servo writing process remains reliable under high-speed production conditions
3Manufacturing precision
If external media writers or servo writing machines are used for precise spiral writing, then spiral positioning accuracy is improved, but manufacturing cost and setup time increase
Solution Approach 1:
The patent enables the HDD to write its own servo spirals using its internal actuator and read/write heads without requiring external media writers or servo writing machines. The drive uses its own servo system to position and write the spirals, eliminating the need for complex external equipment while achieving sufficient precision through iterative refinement and feedback control
Solution Approach 2:
The patent replaces complex external mechanical positioning systems with the HDD's own electronic servo control system. By using software-based velocity control and feedback mechanisms, the system achieves precise spiral writing without requiring external precision actuators or mechanical push pins, thereby reducing device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the reliability of the spiral-based self-servo writing process by ensuring precise spiral spacing and synchronization, reducing the need for rework and improving manufacturing efficiency in high-volume production.
Implementation Method 1
a first read sensor and a second read sensor, such as a magnetic head configured to perform two-dimensional magnetic recording (TDMR)... with the first read sensor, detecting a servo spiral formed on a disk; with the second read sensor, detecting the servo spiral
Data Source
AI summary
A method of determining radial position of a magnetic head that includes a first read sensor and a second read sensor includes: with the first read sensor, detecting a servo spiral formed on a disk; with the second read sensor, detecting the servo spiral; measuring a time interval between when the servo spiral is detected by the first read sensor and when the servo spiral is detected by the second read sensor; and based on the time interval, determining a radial position of the magnetic head relative to the disk.